This invention relates to a fuel cell system provided with a fuel cell which produces electric power by making utilization of hydrogen gas. More specifically, the invention provides a fuel cell system capable of preventing water recovered from such a type of fuel cell from decaying.
With recent increasingly growing recognition of the importance of the global environment protection, fuel cell systems which are small in size but are capable of producing electric power at high levels of efficiency have attracted attention. In addition, when a fuel cell system produces electric power, thermal energy is generated. Accordingly, it is hoped that high levels of energy utilization efficiency are achieved through the use of such thermal energy.
Most of the fuel cell systems of the above-described type use hydrogen for fuel and generate electric power. However, the infrastructure needed for supplying hydrogen to fuel cell systems has still not been provided at present. Consequently, the following procedure has been employed commonly. That is to say, the procedure uses fossil fuels such as natural gas, and hydrogen gas is generated by causing a reforming reaction to take place in the fuel cell system.
Besides, the above-mentioned reforming reaction requires the provision of water, which means that it is very important to secure a water supply source which supplies water to a fuel cell system. In the case where a water infrastructure is always used as a water supply source, the removal of component parts of calcium, chlorine et cetera from the water supplied from the water infrastructure is required. To this end, the fuel cell system has to have a water purifying means (e.g., ion exchange resin) more powerful than usual. This necessitates the execution of regular maintenance work on the water purifying means. As just described, the arrangement that water is always supplied from a water infrastructure gives rise to many disadvantages. In the light of this, for the case of a fuel cell system of a so-called distributed type that is installed in the vicinity of an area in demand of electric power and thermal energy, the procedure of recovering water generated in the inside of the system and making utilization of it, i.e., the water self-supplying procedure, has been employed often.
However, the water recovered in the inside of the fuel cell system does not contain any bactericidal substances such as the component parts of chlorine but does contain undesirable germs and their necessary nourishment. This increases the possibility that the recovered water decays. If the recovered water decays, this will give rise to flow path blockage in a water recovering portion or in a water supply portion, thereby producing problems with the water supply.
With a view to eliminating these drawbacks, there have been made several proposals. For example, there is a first method in which organic materials are decomposed and germ-eradicated by blowing ozone generated by an ozone generator into the recovered water. In addition, in a second method, various germs are eradicated by exposure of the recovered water to ultraviolet irradiation. Furthermore, there is proposed a third method in which, in order to prevent the recovered water from decaying, both a water recovering portion and a water supply portion are formed of material having an antibacterial action. For example, Japanese Patent Application Kokai Publication No. 1996-22833 discloses an exemplary case in which both a water recovering portion and a water supply portion are formed using metal having an antibacterial action.
However, both the first method (i.e., ozone blowing) and the second method (i.e., ultraviolet irradiation) find it difficult to utterly decompose and remove organic materials contained in the recovered water. Besides, if there are members and pipes which come to contact with ozone or are irradiated with ultraviolet light and which are formed of resin material, these components deteriorate significantly, therefore producing another problem that water leakage will occur. Furthermore, if ozone blowing or ultraviolet irradiation has not been carried out over a long period of time, this increases the possibility that the degree of water decay becomes progressively worse by residual component parts. For example, when the fuel cell system has been taken out of operation for a long period of time, neither ozone blowing nor ultraviolet irradiation can be carried out, therefore producing the problem that the decay of water becomes progressively worse.
On the other hand, in accordance with the third method, both an apparatus for water recovery and an apparatus for water supply are formed of material having an antibacterial action. This makes it possible to effectively preventing the recovered water from decaying. However, since the elution of antibacterial component parts cannot be controlled, the result may be that antibacterial effects cannot be obtained as expected depending the use conditions. In addition, there is a likelihood that antibacterial effects are not exhibited at all depending on the type of bacteria. Besides, there is another problem that the load to a purifying means for recovered water purification, especially the load to an ion exchange resin, increases.